In radiosurgery, very intense and precisely focused doses of radiation in a beam from a source outside a patient's body are delivered to a target region in the body, in order to destroy tumorous cells. Typically, the target region consists of a volume of tumorous tissue. Radiosurgery requires an extremely accurate spatial localization of the targeted tumors. Radiosurgery offers obvious advantages over conventional surgery, during which a surgeon's scalpel removes the tumor, by avoiding the common risks and problems associated with open surgery. These problems include invasiveness, high costs, the need for in-hospital stays and general anesthesia, and complications associated with post-operative recovery. When a cancerous tumor is located close to critical organs, nerves, or arteries, the risks of open surgery are even greater.
As a first step in performing radiosurgery, it is necessary to deteIn1ine with great precision the location of tumors and any surrounding critical structures, relative to the reference frame of the treatment device. CT and MRI scans enable practitioners to precisely locate a tumor relative to skeletal landmarks or implanted fiducial markers. However, it is also necessary to control the position of the radiation source so that its beam can be precisely directed to the target tissue, with control of propagation in and through other body structures.
To effect such beam position control, stereotactic frames have been developed and used in the past for treatment of brain tumors. Stereotactic frames are rigid metal frames that are attached to the patient's skull and locked in place to provide a frame of reference for the surgeon during CT/MRI imaging, and for subsequent therapeutic treatment. A stereotactic frame is typically attached to the patient prior to scanning/imaging. The frame must remain in place while the surgeon is developing a computerized treatment plan, as well as during the actual treatment. During treatment, an x-ray or gamma ray source is precisely positioned with respect to the frame, so that the radiation can be administered according to the treatment plan.
While there are well-developed methods for attaching stereotactic frames to the skull for brain tumor treatment, attaching these frames to anatomical regions other than the skull in order to establish a stable frame of reference is too difficult to be practical. As one prior art example, a stereotactic frame that was deliberately constructed for the rest of the body (outside the head/neck region) required screws to be placed in the pelvis, incisions to be made along the spine to accommodate spinal clamps, and ten hours of general anesthesia to be administered to the patient while the frame was being attached to the patient, CT imaging performed, and radiosurgery undertaken. It is clearly not practical to perform such frame-based radiosurgery on areas other than the skull, and therefore the use of frame-based radiosurgery has so far been restricted to the treatment of intra-cranial tumors.
Despite the advantages of radiosurgery over open surgery, including significantly lower cost, less pain, fewer complications, no infection risk, no general anesthesia, and shorter hospital stays (most radiosurgical treatments are outpatient procedures), frame-based radiosurgery has a number of drawbacks. These drawbacks mostly relate to the use of the stereotactic frame. A stereotactic frame causes pain to the patient, since it has to be attached with screws. Also, a frame cannot be easily re-attached in precisely the same position for a subsequent radiation procedure, so that frame-based radio surgical treatment is limited to smaller tumors (generally less than about three centimeters in diameter) that can be treated in a single procedure. Moreover, the frame must remain in place from the time of diagnostic CT and/or MRI scanning, through the entire period of treatment, which may extend over a multi-day period. Finally, the biggest drawback is that frame-based radiosurgery cannot be used for tumors located outside of the head and neck region, because of the above-described difficulty of attaching these frames to anatomical regions other than the skull. Frame-based radiosurgery therefore cannot be used to treat ninety percent of all solid tumors, because they occur outside of the head/neck region.
These drawbacks have lead to the development of a frameless stereotactic radiosurgery system, exemplified by the CyberKnife system (henceforth “CyberKnife”) made by Accuray, Inc., Sunnyvale, Calif. CyberKnife is an image guided robotic system which eliminates the need for the rigid stereotactic frames described above, and enables the treatment of extra-cranial tumor sites. CyberKnife provides numerous advantages compared to conventional stereotactic radiosurgery systems, including but not limited to: ability to treat tumors throughout the body, not just those located within the head/neck region; increased access to, and coverage of, any target volume; ability to treat tumors that are larger than about three centimeters in diameter; minimal constraints on patient set-up; ability to deliver a plurality of fractionated treatments; and enhanced ability to avoid damaging critical structures.
CyberKnife includes a robotic system onto which an x-ray linear accelerator (“linac”) is mounted, and a controller. The linac is adapted to selectively provide a precisely shaped and timed radiation beam. The controller uses CT and possibly MRI data, or other types of image data, that define the target tissue and important other bodily structures, together with treatment planning and delivery software to identify a series of landmarks within the treatment region, prior to surgery. CyberKnife may further include a stereo x-ray imaging system, which during treatment repeatedly measures the location and orientation of these landmarks relative to the linac. Prior to the delivery of radiation at each delivery site, the controller directs the robotic system to adjust the position and orientation of the linac in accordance with the measurements made by the x-ray imaging system, so that a desired series of radiation beams can be applied to the body, optimally dosing the target tissue while minimizing radiation to other body structures. In this way, CyberKnife allows accurate delivery of high doses of radiation, without requiring a stereotactic frame.
It is important to ensure that during the successive positionings of the linac during a treatment, the robotic system does not collide with objects (for example, parts of the patient's body, its own structure, or other equipment in the treatment room). Since patient setup is minimally constrained by a frameless radiosurgery system, it is difficult to have complete knowledge of the patient's body position when preparing a treatment plan, particularly regarding their arms and legs. An obstacle detection/collision avoidance system would therefore be desirable in frameless radiosurgery systems such as the CyberKnife,
Because of its ability to deliver fractionated treatments, CyberK11ife is well adapted for radiotherapy, as well as for radiosurgery. The term radiotherapy refers to a procedure in which radiation is applied to a target region for therapeutic, rather than necrotic, purposes. The amount of radiation utilized in radiotherapy is typically about an order of magnitude smaller, as compared to the amount used in radiosurgery. Radiotherapy is frequently used to treat early stage, curable cancers. In addition to delivering radiation to cancerous tissue, radiotherapy systems generally also irradiate a certain amount of normal tissue surrounding the tumor. Typically, a series of relatively small doses are delivered over a number of days. Each radiation dose not only kills a little of the tumor, but also creates some collateral damage to healthy surrounding tissue, which however usually heals by itself, because it has a greater ability to repair, compared to cancerous tissue.
A collision avoidance system, referred to above, would also be desirable when CyberKnife is being used for radiotherapy, as well as for radiosurgery. For convenience, the term “radiosurgery” in this application shall henceforth mean “radiosurgery and/or radiotherapy.”
The present invention provides a frameless radiosurgery system having a collision avoidance subsystem.
In an exemplary embodiment, a frameless radiosurgery system in accordance with the present invention includes an x-ray source, and a robot. The robot includes an arm assembly extending from a base unit. The x-ray source, which in a preferred form is a linac, has an emission head mounted at a distal end of the arm assembly. The x-ray emission head is adapted for selectively emitting an x-ray beam along a beam axis. The arm assembly may be articulated (i.e., have a series of rigid elements linked by rotatable couplings), may be flexible (i.e., have a series of rigid or flexible elements linked by flexible couplings), or may be a combination of both articulated and flexible portions.
The radiosurgery system further includes an associated controller for selectively orienting the x-ray emission head whereby the x-ray beam extends along a succession of treatment axes. The radiosurgery system further includes a collision avoidance subsystem, including means for preventing the x-ray emission head and the arm assembly from effecting a collision with an object in one or more pre-defined exclusion zones.
In one exemplary embodiment of the invention, the collision avoidance subsystem includes a light source (such as a laser or an LED (light-emitting-diode) effective to establish a substantially planar (or sheet-like) light beam between the exclusion zone and the emission head. The planar light beam may be fan-shaped. In this embodiment, the controller is responsive to observation of an object extending through the light beam, to interrupt any further motion of the head toward the exclusion zone. The light source may be fixedly positioned with respect to the x-ray emission head, defining an exclusive zone that “travels” with the head. Alternatively, the light source may be fixedly positioned with respect to the base unit of the robot, for example by being mounted on a wall of the treatment room, defining an exclusive zone that is fixed with respect to the treatment room.
In another embodiment of the invention, the collision avoidance subsystem includes a least one optical emitter-receiver pair that is effective to detect the breaking of a light beam when an object extends into the one or more exclusion zones. The optical emitter is a light source, as described in paragraph 15 above. The optical receiver is constructed and arranged to receive light that 1) has reached an object that has intruded into one or more of the exclusion zones, and 2) is back-scattered from the object.
In another embodiment of the invention, the collision avoidance subsystem includes a laser range finder that can detect movement of an object into a light beam. The laser rangefinder includes a transmitter that generate laser light and transmits the light toward one or more exclusion zones, and a receiver/photodetector for receiving and detecting laser light that is backscattered from any object that intrudes into the one or more exclusion zones. The laser range finder includes means for determining, from the received back-scattered laser light, the distance to the object.
In another embodiment of the invention, a plurality of exclusion zones may be defined. In other words, multiple “layers” of exclusion zones may be defined. In one of many possible exemplary embodiments, a first “shell-like” exclusion zone may be defined which slows down the motion of the head. In this exemplary embodiment, a second exclusion zone may be defined, which completely stops any further motion of the head, when the head reaches one or more boundaries between the first exclusion zone and the second exclusion zone. In another embodiment of the invention, at least one of the exclusion zones is not a static zone, but rather is a variable dimension exclusion zone. In another embodiment of the invention, the collision avoidance subsystem includes an array of acoustic transducers fixedly coupled to the x-ray emission head. Each of the transducers transmits a succession of acoustic pulses along a transmission axis extending from the head, and detects acoustic energy backscattered along the transmission axis from an object disposed along the transmission axis. The beam axes are mutually aligned whereby cross-sections of adjacent pairs of the pulses transverse to the transmission axis are contiguous at a predetermined distance from the head. In this embodiment, the collision avoidance subsystem includes means for determining, from the received backscattered acoustic energy, the distance between the head and the object.
The collision avoidance subsystem further includes means for inteJ11lpting, in response to the determined distance being at or less than a predetermined value, any further motion of the head toward the exclusion zone.
In another embodiment of the invention, the collision avoidance subsystem includes a sensor disposed on a surface of the articulated arm assembly. The sensor is operative to generate an alarm signal upon impact of the sensor with an object, during motion of the arm assembly and/or the x-ray emission head. The subsystem further includes means responsive to the alaIn1signal to interrupt any further motion of the arm and/or head. The sensor may be a tactile sensor, or other type of sensor adapted for proximity sensing. By way of example, the sensor may consist of a fluid-filled bladder, and a pressure transducer coupled to the bladder, in one embodiment of the invention. In other embodiments, the sensor may be an infrared (IR) sensor, or an electrostatic capacitance sensor.
In any of the above described collision avoidance systems, the detection of breach of the exclusion zone and the system's response to such detection may be automatic (e.g., under control of the controller) or may be manually implemented (e.g., when a human observer detects a breach, that observer initiates the system response (e.g., halting further advance of the head).